Avoid NPE

(applying suggestion from code review)

Co-authored-by: Sören Domrös <[email protected]>

plugins/org.eclipse.elk.graph.json/src/org/eclipse/elk/graph/json/JsonImporter.xtend

@@ -580,10 +580,10 @@ final class JsonImporter {
         do {
             if (ancestor !== null) {
                 ecm = ancestor.getProperty(CoreOptions.JSON_EDGE_COORDS) ?: EdgeCoords.INHERIT
+                ancestor = ancestor.getParent
             } else {
                 ecm = EdgeCoords.CONTAINER
             }
-            ancestor = ancestor.getParent
         } while (ecm === EdgeCoords.INHERIT)
         return ecm
     }